Add an easy way to quickstart the development environment

Add setup.py + tox + a quickstart script.

The quickstart script creates a virtualenv and downloads the packages listed in setup.py. Tox seems to require that a setup.py is present. This should reduce the hassle in finding the correct versions of the different packages etc. and installing them.

Also use the pure-Python Whoosh search engine if xapian is missing (The Xapian+Haystack combination is somewhat painful to install).